Hiding the keyboard looks glitchy

When hiding the keyboard, there is a short moment when the background behind the app (sometimes the wallpaper, sometimes another app) is visible, which looks quite glitchy. I believe this is because resizing the app window is not in perfect sync with the hiding of the keyboard.

Some ideas for fixing this:

• Always have a black layer behind the open app, so even if the resizing lags a bit you don't see anything unrelated behind the app
• Use a revealer for showing/hiding the keyboard. This would give the app time to resize, and we'll want this sooner or later anyway because it's nicer UX wise

Not sure if this is a Phosh or Squeekboard issue, feel free to move it if appropriate.